Metal complexes each act as a catalyst in a redox reaction involving electron transfer such as an oxygenation reaction, an oxidative coupling reaction, a dehydrogenation reaction, a hydrogenation reaction, an oxide decomposition reaction, or an electrode reaction, and are each used in the production of an organic compound or polymer compound. In addition, each of the metal complexes has been recently used as a phosphorescent complex for an organic EL material. Further, the metal complexes are used in various applications including additives, modifiers, cells, and sensor materials.
In particular, as for a redox reaction catalyst, Schiff base type metal complexes are known to have the highly-active and highly-selective catalytic abilities. For example, Org. Biomol. Chem., 2005, 3, 2126 describes that an optically active Schiff base type complex is used as a catalyst to oxidize the double bond of styrene so that an asymmetric cyclopropanation reaction may occur, and the asymmetric reaction may proceed favorably. In addition, Inorg. Chem., 2001, 40, 1329 describes that the production of water by the electrolytic reduction of oxygen is performed by using a Schiff base type metal complex.
However, the metal complex disclosed in Org. Biomol. Chem., 2005, 3, 2126 involves the possibility that when the metal complex is used as a catalyst, the catalyst is destabilized under heating, and hence its activity lowers. Further, the catalyst is used in a limited range of applications owing to the possibility that the catalyst is destabilized also in the presence of a strong acid. As described above, a metal complex that has been conventionally disclosed has the potential to be decomposed under some reaction conditions.